A method for preparing pure, gaseous carbon dioxide and an apparatus to be used therewith

Abstract: The invention relates to a method for preparing pure, gaseous CO₂ from a gaseous CO₂-containing product (2) having a lower degree of purity than the final product, by compressing (4) and cooling (5) the gaseous basic material, whereupon the gaseous impurities are discharged and the purified liquid CO₂ (27) is used as a cooling medium for cooling the gas mixture which is used as the basic material, whereby the gas mixture is compressed (8) to a pressure of 40 - 65 bar before the cooling step (12) is carried out. The invention furthermore relates to an apparatus for carrying out this method.

Description: The invention relates to a method for preparing pure, gaseous CO 2 from a gaseous CO 2 -containing basic material having a lower degree of purity than the final product, by compressing and cooling the gaseous basic material, liquefying it by using purified liquid CO 2 as a cooling medium whereupon the gaseous impurities are discharged from the liquefied gaseous basic material and the vaporised purified liquid CO 2 is supplied to a consumer. The invention furthermore relates to an apparatus for carrying out said method; said apparatus consisting of at least two compressors, two coolers and purification equipment which are interconnected via piping suitable for that purpose. A method and an apparatus of this type are known from European Patent Application No. 194,795. The method as it is known from the aforesaid European Patent Application shows the preparation of liquid carbon dioxide, whereby the pure liquid carbon dioxide formed in the course of the implementation of the method is used as the cooling medium for the preparation of gaseous carbon dioxide. The use of liquid carbon dioxide as a cooling medium is for example important in a beer brewing plant, because if other, usual cooling agents are used, such as ammonia or chlorofluorocarbons, there is a danger that the desired pure carbon dioxide as the final product is contaminated with cooling agent. Although liquid carbon dioxide formed in the course of the preparation is used as the cooling agent in the aforesaid European Patent Application, another cooling agent is furthermore used in cooling unit 20, as shown in Figure 1 of the aforesaid European Patent Application. Furthermore it has appeared to be possible to enhance the efficiency of the preparation process of purified, gaseous carbon dioxide in comparison with the efficiency that can be achieved in practice by using the aforesaid known method. The method according to the invention is characterized in that the compression of the gaseous basic material is performed in at least two stages to a final pressure of 40 - 65 bar, said purified liquid CO 2 is expanded to the suction pressure of the compressor of the last stage, whereupon the gaseous CO 2 thus obtained is fed back as flash gas to the supply pipe of the compressor of the last stage, said liquid purified CO 2 fraction is used to liquefy said gaseous basic material. Furthermore it is to be preferred to use cooling water, ice water or another cooling agent, such as alcohol or propene glycol, to the exclusion of chlorofluorocarbons or ammonia, besides liquid, purified CO 2 as the cooling agent. The increasing of the pressure of gaseous, impure CO 2 to a pressure of 40 - 65 bar takes place immediately before liquid carbon dioxide is formed wherein the compression of the gaseous basic material is performed in two stages, in the first compressing step to a pressure of about 14-22 bar and in the second compressing step to a pressure of 40-65 bar. The invention will be explained in more detail with reference to the following description, wherein reference is made to the appended drawing, in which: Figure 1 shows a block diagram of the various steps for carrying out the method according to the invention. Figure 1 illustrates in a block diagram the steps for carrying out the method according to the invention, whereby air-containing carbon dioxide in gaseous, impure condition is obtained in vessel 2. The carbon dioxide obtained in vessel 2 may have a degree of purity of about 80% and contains air to the amount of about 20 per cent by volume. From this carbon dioxide having a purity of at least about 99.9 per cent by volume is obtained, which may be used in for example the preparation of beer. The unpurified carbon dioxide is caught in the receptacle 3 and subjected to a first compressing step in compressor 4 to about 14 - 22 bar. After cooling, drying and absorbing impurities such as interfering aromatics in parts 5, 6 and 7 respectively, an important step according to the invention takes place in compressor 8, where the prepurified gas is further compressed to a pressure of 40 - 65 bar. After leaving the compressor 8 the compressed gas is led to reboiler 9, via pipe 22, without further cooling, said reboiler 9 being in communication with the collecting vessel 10, in which compressed liquid carbon dioxide is collected at a pressure of 40 - 65 bar. From the reboiler 9 the compressed CO 2 is led to cooler 12 via pipe 23, where it is cooled with ice water. Cooler 12 is in communication with the heat exchanger 13, which is cooled with liquid CO 2 from the collecting vessel 11, Which is supplied to an apparatus 14 for expanding carbon dioxide, so that a temperature of for example - 45 °C is produced at 14. The heat exchanger 13 is of a pipe-jacket type, whereby the expanded carbon dioxide is supplied via pipe 27 and discharged via pipe 28, whilst the carbon dioxide to be cooled is supplied to the heat exchanger 13 via pipe 25 and discharged via pipe 24a. The gaseous impurities, such as air, are discharged from the heat exchanger 13 via pipe 26, so that liquid carbon dioxide is discharged to the stripper 16 via the pipe 24a, in order for the liquid CO 2 to be purified. Said purified liquid CO 2 is collected in the collecting vessel 10. When the level in vessel 10 rises, the valve 41 is opened, as a result of which said liquid CO 2 expands from a pressure of 40 - 65 bar to a pressure of 14 - 22 bar. The gaseous CO 2 thus obtained is fed back as flash-gas to a place before the compressor 8 via pipe 21, whilst the liquid CO 2 remains behind. The gaseous carbon dioxide which is formed at 14 is supplied, as a gaseous carbon dioxide in purified condition, to the place of consumption 1 of purified CO 2 via the pipe 29 and the valves 43 and 40, whereby it is possible to feed back part of said gaseous carbon dioxide to the starting point for the apparatus near the receptacle 3 in case there is insufficient demand for purified CO 2 at 1 or if additional cooling is necessary in cooler 13. Via pipe 31 purified carbon dioxide is furthermore supplied to the place of consumption 1 by supplying liquid carbon dioxide to the evaporator 15, whereupon gaseous, purified carbon dioxide is formed. The method may furthermore be controlled by means of various valves and cocks 40 indicated in the drawing. It will be apparent, however, that these are shown by way of indication only and that the principle of implementing the method according to the invention can only be derived from the block diagram. The invention furthermore relates to the apparatus for implementing the method, whereby the apparatus is partly known from European Patent Application No. 194,795. The apparatus according to the invention is characterized in that two compressors (4, 8) are placed before the coolers (12, 13), said coolers (12, 13) being connected to an expansion means (10, 41, 11) for preparing flash gas and purified liquid CO 2 , wherein a pipe (21) is provided for feeding back flash gas to the supply pipe of the compressor (8) of the last stage and wherein a pipe (31) is provided for supplying purified carbon dioxide to said second cooler (13) for liquefying the gaseous basic material.

Claims: A method for preparing a pure, gaseous CO 2 from a gaseous CO 2 -containing basic material having a lower degree of purity than the final product, by compressing and cooling the gaseous basic material, liquefying it by using purified liquid CO 2 as a cooling medium, whereupon the gaseous impurities are discharged from the liquefied gaseous basic material and the vaporised purified liquid CO 2 is supplied to a consumer, characterized in that the compression of the gaseous basic material is performed in at least two stages to a final pressure of 40 - 65 bar, said purified liquid CO 2 is expanded to the suction pressure of the compressor of the last stage, whereupon the gaseous CO 2 thus obtained is fed back as flash gas to the supply pipe of the compressor of the last stage, said liquid purified CO 2 fraction is used to liquefy said gaseous basic material. A method according to claim 1, characterized in that besides liquid, purified CO 2 also ice water is used as the cooling agent, to the exclusion of chlorofluorocarbons and ammonia. A method according to claims 1-2, characterized in that the compression of the gaseous basic material is performed in two stages, in the first compressing step to a pressure of about 14-22 bar and in the second compressing step to a pressure of 40-65 bar. An apparatus for carrying out the method according to claim 1, said apparatus consisting of at least two compressors, two coolers and purification equipment, which are interconnected via piping suitable for that purpose, characterized in that two compressors (4, 8) are placed before the coolers (12, 13), said coolers (12, 13) being connected to an expansion means (10, 41, 11) for preparing flash gas and purified liquid CO 2 , wherein a pipe (21) is provided for feeding back flash gas to the supply pipe of the compressor (8) of the last stage and wherein a pipe (31) is provided for supplying purified carbon dioxide to said second cooler (13) for liquefying the basic material.

Inventors: HAFFMANS HUBERTUS ERNEST FERDI, HAFFMANS, HUBERTUS ERNEST FERDINAND MARIE
Applicants: HAFFMANS BV, HAFFMANS B.V.
Application year: 1994
Main classification: F25J3
IPC codes: F25J3, C12F3, C01B31